The overall objectives of this investigation are to identify the location of the follicle stimulating hormone (FSH) in the testes of immature and adult rats. The physiological significance of these findings will be elucidated by studying the sites of FSH under various experimental conditions. Investigations planned for the next year include in vitro studies of enriched Sertoli and Leydig cell populations to determine if these cells possess binding sites for anti-FSH.